Printing machines generally comprise a paper transfer path, along which paper can be moved from one location within the printer to another. For example, in some embodiments, paper may be picked up from a paper input tray, transported via a paper transport mechanism to an impression drum, where heated ink is transferred onto the paper, and finally transported to a paper output of the printer. Other paper handling mechanisms, such as duplexing, may additionally take place within the printer.
There is a problem with such a printer in that paper may stick or jam within the machines or arrive at an unwanted location.
In particular, in some existing printer machines heated ink is transferred onto a sheet of paper, while it is on the impression drum, by an intermediate transfer media (ITM) drum. The ITM drum typically, in some embodiments, comprises a charged blanket, which is heated by an heating unit external to the ITM drum. Ink on the blanket is liquefied (or kept liquid) by the heat of the blanket, for transfer to the sheet of paper. It is possible during printing for a sheet of paper to stick or adhere to the ITM drum, rather than being carried away to the paper output, and to arrive without warning at the external heating unit. This is undesirable, as the paper may be scorched or burnt by the external heating unit. Damage may be caused to the printer if the paper is not removed sufficiently quickly, or if the heating unit is not turned off. Furthermore, such paper jammed within the machine may cause the printer to operate incorrectly, resulting in spoiled, incorrectly printer paper being output by the printer. Such paper must be removed.
In order to remove paper that has become stuck in an undesired location, one must know that it is there. It is also desirable to find out that paper has arrived at the undesired location, such as the external heating element, before too many incorrect sheets have, been printed, and before damage is caused to the machine.
According to one aspect of the invention we provide a paper sensor as described in the claims.
Such a paper sensor provides an indication that paper has arrived at the external heating element, allowing the printer to be immediately switched off, avoiding the possibility of machine damage. The sensor additionally provides a physical barrier that prevents paper from moving inside the heating unit.
A printer comprising a paper sensor and a method of paper sensing are also described.
According to another aspect of the invention there is provided a paper sensor comprising a grill and a micro-sensor, the micro-sensor being operable to detect an increase in pressure on the grill (or a differential pressure across the grill). The micro-sensor may comprise a piezoelectric sensor. The increase in pressure may be due to a sheet of paper obstructing a flow of air through holes in the grill.
An embodiment of the invention will now be described, by way of example only, with reference to the following drawings.